Solid State Relay: types, practical application, wiring diagrams

Classic starters and contactors are gradually fading. Their place in automotive electronics, consumer electronics and industrial automation takes the solid state relay.

This semiconductor device can have different designs and connection schemes, which depend from and scope of the instrument.

Apparatus SSR

Modern solid-state relay (SSR) are modular semiconductor devices, electric switches are power.

Key operating components of these devices presents triacs, thyristors or transistors. TTP have no moving parts than different from electromechanical relays.

The size of the solid-state relay is largely dependent on the maximum load and the opportunity to remove heat by convection heat transfer, and

Internal Design of these devices may vary greatly depending on the type of load and adjustable circuitry. The simplest solid-state relays include components:

1. Input unit fuse.
2. Trigger circuit.
3. Optical (galvanic) isolation.
4. Switching unit.
5. Protective circuit.
6. Node Output to the load.

The input unit SHT is a primary circuit connected in series with a resistor. Fuse in this circuit is incorporated optionally. input node task - taking a control signal and sending commands to the switching load switches.

When an alternating current for controlling the separation of the main chain and galvanic isolation is used. From its devices depends largely on the principle of the relay. Responsible for the trigger input signal processing circuit may be included in the optical isolator unit, or arranged separately.

Protective member prevents the emergence of congestion and error, because in case of failure of the device may be damaged and the connected equipment.

The main purpose of solid-state relays - closing / opening the electric network via the weak control signal. Unlike the electromechanical counterparts, they have a more compact shape and do not produce during operation characteristic clicks.

The operating principle of TTP

SSR work is quite simple. Most of the TTP is designed for automation control networks 20-480 V.

Optical isolation allows you to create management signals the minimum power, which is critical for sensors operating from independent power supply

In the classical version in the housing includes two contacts switched circuit and two control wires. Their number may vary as the number of connected phases. Depending on whether the voltage in the control circuit turns on and off the primary load semiconductor elements.

A special feature is the presence of SSRs Finite resistance. If contacts in electromechanical devices are separated completely, in the absence of solid in the loop current provided by the properties of semiconductor materials. Therefore, at high voltages may cause small leakage currents which may adversely affect the operation of the connected machinery.

Classification of solid state relays

Scope of application of the relay varied, and therefore their design features can vary greatly, depending on the needs of the automatic scheme. TTP is classified by the number of connected phases, the operating current mean structural features and the type of control circuit.

According to the number of connected phases

Solid state relays are used as a part of home appliances, and industrial automation with an operating voltage of 380V. Therefore, the semiconductor devices are divided according to the number of phases, on:

• single-phase;
• three-phase.

Single-phase SSR allow you to work with currents of 10-100 or 100-500A. Their control is performed using an analog signal.

For three-phase relay it is recommended to connect the wires of different colors, so you can attach them correctly when installing the equipment

Three-phase solid-state relay can pass a current in the range 10-120A. Their device involves reversing the principle of operation which provides reliable regulation simultaneously several electrical circuits. Often three-phase SSR is used for the operation of an induction motor. Its electric system management necessarily includes a quick fuses due to high inrush currents.

By type of operating current

SSRs can not be configured or reprogrammed so that they can function properly only when a certain range of electric parameters network. Depending on the needs of TTP associated circuits can be controlled with two power modes:

• DC;
• variables.

Similarly, we can classify the TTP and mean active load voltage. Most relays in household appliances operate with variable parameters.

Direct current is not used as the primary source of electrical power no country in the world, so the relay of this type have a narrow scope of application

Devices with a constant drive current characterized by high reliability and are used for voltage regulation 3-32 V. They withstand a wide temperature range (-30.. + 70 ° C) without significant change in performance.

Relays, controls an alternating current have a control voltage V or 3-32 70-280 V. They have low electromagnetic interference and a high response speed.

On design features

Solid state relays are often mounted to a common electrical panel apartments, and many models have a mounting block for mounting on DIN-rail. Furthermore, there are special radiators, which are located between the TTF and the support surface. They allow the appliance to cool under heavy loads, while maintaining its performance.

Relay mounted on DIN-rail preferably via a special bracket, which has an additional function - removes excess heat during operation of the device

Between the relay and the radiator is recommended to apply a layer of thermal grease, which increases the contact area and increases heat transfer. There are TTP, designed for wall mounting conventional screws.

By type of management scheme

It is not always working principle of the relay controlled appliances it requires an instant response. Therefore, several manufacturers have developed TTF control circuits that are used in various fields:

1. Control "through zero". Such an embodiment involves driving SSR triggering only when a voltage value equal to 0. Used in devices with capacitive, resistive (heaters) and a weak inductive (transformer) load.
2. Instant. Used as necessary a sharp operation of the relay when the control signal.
3. Phase. It involves regulation of the output voltage by changing the control current parameters. It is used to smooth changes in the degree of heat or light.

Solid state relays are different and in many other, less important parameters. Therefore, when buying TTP is important to understand the scheme of plug-in technology in order to acquire the most appropriate to it an adjusting device.

Be sure the power supply must be provided, because the relay has a service life that is rapidly consumed at frequent overloads.

Advantages and disadvantages of TTP

Solid State Relays knowingly displace from the market of conventional starters and contactors. These semiconductor devices have many advantages over electromechanical analogs that cause consumers to stop the choice on them.

Relay IC is compact and heavily limited by the maximum current is skipped. They are fixed preferably by soldering special legs

These advantages include:

1. Low power consumption (90% less).
2. Compact dimensions, allowing to mount the device in a limited space.
3. High speed start-up and shutdown
4. Reduced noise operation, there is no characteristic for the electromechanical relay clicks.
5. It is not intended to maintenance.
6. Long service life thanks to the resource in the hundreds of millions of operations.
7. Due to the vast possibilities of modification of electronic components, TTP have expanded the scope of application.
8. Absence of EMI when triggered.
9. Excludes damage of the contacts due to their mechanical shock.
10. The lack of direct physical contact between the control and switching circuits.
11. The possibility of load control.
12. The presence of pulse TTP automatic circuit to protect against overload.
13. Ability to use in explosive environments.

These advantages of solid-state relays are not always sufficient for the normal operation of equipment. That is why they have not yet completely replaced electromechanical contactors.

For stable operation, high-power solid-state relay important effective heat dissipation, because at elevated temperatures dramatically distorts the load voltage

TTP have disadvantages that do not allow them to be used in many cases. These include:

1. The inability of most devices with voltages above 0.5 kV.
2. High price.
3. Sensitivity to high currents, especially in the start-up of electric circuits.
4. Restrictions on use in damp conditions.
5. A critical lowering of performance at temperatures below 30 ° C and frost above 70 ° C heat.
6. Compact housing results in excessive heating device stably at high loads, which requires the use of special devices the passive or active cooling.
7. Ability melting device from heating during a short circuit.
8. Microcurrents closed relays can be critical to the operation of the equipment. For example, in the connected fluorescent lamps may flash periodically network.

Thus, solid state relays have certain application. In the high-voltage circuits of industrial equipment their use severely restricted due to imperfect physical properties of semiconductor materials. However, in household appliances and automotive industries TTP has a strong position due to its positive properties.

Possible circuit connections

Wiring diagrams of solid state relays can be varied. Each electrical circuit is constructed, based on the characteristics of the connected load. The additional circuitry can be added preservatives, controllers, and control devices.

Due to the fact that the control and load circuit in the unit do not overlap, their electrical characteristics may vary any parameter

Next will be presented to the most simple and common scheme TTP connection.

• normally open;
• with associated circuit;
• normally closed;
• the three-phase;
• reversible.

Under a normally open (open) the relay is meant, wherein the load is energized in the presence of a control signal. That is, the connected equipment is in the open position when de-energized inputs 3 and 4.

Before buying relay necessary to determine the required type of its initial state (open or closed) to ensure proper operation of the equipment connected

Under a normally closed relay is meant, wherein the load is energized in the absence of the control signal. That is, the connected equipment is in working condition when de-energized inputs 3 and 4.

There is a connection diagram of the solid-state relays, in which the control voltage and the load equally. Such a method can be used simultaneously to work in networks of direct and alternating current.

Three-phase relay connect somewhat different principles. The contacts may be connected in "Star" variants, "triangle" or "star with neutral".

Selection of a three-phase relay connection circuit largely depends on the characteristics of the work equipment, connected thereto as a load

Reverse solid state relays are used in electric motors in the corresponding mode. They are manufactured in a three phase embodiment and includes two control loops.

If the relay is important to respect the polarity of the contacts to connect, then the marking will always indicate where to connect the phase and neutral

Collect circuits to TTR is necessary only after a preliminary drawing on paper, because it incorrectly connected devices can be damaged due to a short circuit.

Practical application devices

The scope of the use of solid-state relay is quite extensive. Due to the high reliability and the lack of regular maintenance needs are often placed in hard to reach areas of equipment.

In many relays the connection of the control circuit wires requires a polarity that must be considered in the process of installation of the equipment

The main applications of the TTF are:

• thermoregulation system with heaters;
• maintaining a stable temperature in the processes;
• control of transformers;
• adjustable lighting;
• motor control;
• scheme motion sensors, lighting, photosensors, etc .;
• uninterruptible power supply.

With increasing automation of household appliances solid state relays are becoming more common, and developing semiconductor technology is constantly opening up new application areas.

Useful videos on the topic

Submitted videos to help better understand the operation of solid-state relays and become familiar with how they connect.

Practical demonstration of the simple solid-state relays:

Analysis of types and features of operation of solid-state relays:

Testing of work and the degree of heating TTP:

Assemble electrical circuit of a solid-state relays and transmitter may almost everyone. However, planning the workload requires basic knowledge of electrical engineering, because a wrong connection can lead to electric shock or short circuit. But as a result of right action can get a lot of useful devices in everyday life.